AU768987B2

AU768987B2 - A digital hearing aid with a voltage converter

Info

Publication number: AU768987B2
Application number: AU23530/01A
Authority: AU
Inventors: Henning Haugard Andersen
Original assignee: Widex AS
Current assignee: Widex AS
Priority date: 2000-01-07
Filing date: 2001-01-05
Publication date: 2004-01-15
Anticipated expiration: 2021-01-05
Also published as: US6741715B2; DE60105758D1; WO2001050812A1; CA2396437A1; DK1247426T3; EP1247426B1; JP3847627B2; CA2396437C; US20020196957A1; AU2353001A; ATE277492T1; EP1247426A1; DE60105758T2; JP2003520003A

Abstract

A digital hearing aid comprises a microphone (2), an output transducer (3), a digital signal processor (5) interconnected between the microphone and the output transducer, and a power source (7) including a standard hearing aid battery for the supply of operation voltage for the digital signal processor. At least one of the integrated circuit signal processing parts is designed to operate at a reduced unstabilized operation voltage substantially below a nominal voltage of the battery. A switched step-down voltage converter is connected between the power source and such signal processing parts for lowering the battery voltage to provide the reduced operation voltage.

Description

1 Title A digital hearing aid with a voltage converter Technical Field The present invention relates to a digital hearing aid.

Background Art In its fresh condition a normal hearing aid battery supplies a voltage of about 1.3 V and during its active life the battery can supply current sufficient for the operation of the hearing aid down to a voltage of about 1 V, below which the power supplying capacity of the battery drops rapidly.

In prior art hearing aid technology it is well known to provide operation voltages higher than the nominal battery voltage for certain processing circuits or components, e.g. EEPROM memories and microphone circuits, by means of voltage step-up converters, mostly in the form of switched capacitor networks designed e.g. as socalled charge pump voltage multipliers.

Further examples of use of voltage regulators in hearing aids have been disclosed in the prior art, e.g. a hearing aid comprising a voltage regulator capable of of providing a number of stabilized supply voltages that may be higher or lower than the nominal battery voltage.

Whereas in conventional hearing aid technology the major power supply requirement has been to provide operation voltages sufficiently high for the operation of signal processing circuits and reduction from the nominal battery voltage has only been used for voltage stabilization or provision of reference S* 25 voltages, further lowering of the operation voltage has been considered inconvenient, since it would result in loss of processing speed. In certain parts of digital hearing aids such as a DID output converter, which are responsible for a main part of the power consumption, reduction of the operation voltage would only result in a current increase and provide no saving in power consumption for the V. 30 same output power from the DID converter.

Moreover, in small size hearing aids with a low voltage drop and a current drain of a few mA or even a fraction of mA only, power saving by reduction of the operation voltage has been considered outside interest due to the complex circuitry of a low loss, stabilized series voltage regulator.

35 The general structure of digital hearing aids of this kind is well-known in the Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.

Summary of the Invention The present invention relates to a digital hearing aid comprising a microphone, an output transducer, a digital signal processor interconnected between the microphone and the output transducer, and a power source including a standard hearing aid battery for the supply of operation voltage for said digital signal processor.

The invention is based on the recognition of the fact that, as long as the operation voltage is kept above a defined minimum voltage, some integrated circuit signal processing parts of a digital hearing aid, like e.g. digital filters, are less sensitive to variations in the operation voltage in the sense that such variations would not result in any significant change of performance.

In one aspect, the present invention is a digital hearing aid comprising a microphone, an output transducer, a digital signal processor interconnected between the microphone and the output transducer and a power source including a standard hearing aid battery for the supply of operation voltage for said digital signal processor, characterized in that said digital signal processor comprises at least one integrated circuit signal processing part capable of operating at a 25 reduced power supply voltage within a range below a nominal voltage of said battery and above a defined minimum voltage without significant change of performance, and wherein a switched step-down voltage converter is connected between the power source and said at least one signal processing part for providing said reduced power supply voltage.

30 Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the I exclusion of any other element, integer or step, or group of elements, integers or o steps.

S 35 By lowering of the operation voltage requirement for parts of the integrated signal processing circuits the total current drain and power consumption of the hearing aid is reduced. In particular, this brings substantial benefits in terms of power consumption, when the digital signal processing is operated by large hardware programmed programs, which would otherwise result in significant power consumption.

Preferably, the digital signal processing parts having reduced operation voltage requirements will be designed in MOS or CMOS technology using transistors having a low operating voltage, e.g. a low threshold or pinch-off voltage, compared to bipolar processing circuits as normally used in hearing aids.

Typically, such signal processing parts will comprise circuits that are not stressed with respect to processing speed or output power demand, such as digital filter circuits, whereas more stressed circuits such as an output DID converter or output amplifier may still be supplied with a higher operation voltage.

By suitable design of such signal processing blocks, which are stressed in processing speed, involving e.g. a split-up in more parallel or serial processing blocks, the requirements to processing speed and consequently the operation voltage requirement may be lowered even for such circuit blocks.

Thus, in a preferred embodiment of the hearing aid according to the invention said at least one signal processing part comprises parallel signal processing blocks each operating at said reduced power supply voltage. The reduced operation voltage for the signal processing parts in question would preferably be equal to or below 0.8 V, e.g. in a voltage range of half the nominal battery voltage, such as 0.7 down to 0.4 V, or preferably 0.65 down to 0.5 V.

In a preferred embodiment the switched step-down voltage converter providing the reduced operation voltage or voltages would be a capacitive charge 25 pump converter, which may advantageously be designed to deliver two or more output voltages. However, alternatively also a switched inductor type converter could be envisaged.

It is therefore an advantage of at least one embodiment of the invention to provide a digital hearing aid having a longer active battery life and a reduced 30 power consumption.

0000.- Brief Description of the Drawings In the following the invention will be explained in further detail with reference to the accompanying drawings, of which 35 Fig. 1 is a schematical block diagram of an embodiment of a digital hearing according to the invention, and Fig. 2 shows a first configuration of a switched capacitor voltage step-down converter of the charge pump type for use in the hearing aid shown in fig. 1, Figs. 3 and 4 are simplified diagrams illustrating charge situations in the converter configuration in fig. 2, Fig. 5 shows a second configuration of a switched capacitor voltage stepdown converter of the charge pump type for use in the hearing aid shown in fig. 1, and Figs. 6 and 7 are simplified diagrams illustrating charge situations in the converter configuration in fig. 2.

Best Mode of the Invention The hearing aid schematically illustrated in fig. 1 comprises electric circuits 1 interconnected between oooo *.o 0oo..

WO 01/50812 PCTDKOI/00007 a microphone 2 and an output transducer or receiver 3.

The electric circuits 1 include a signal processing part 5, a control part 6 and a power supply part 7. In a digital hearing aid the signal processing parts will at least comprise an A/D converter for conversion of the analog signal from the microphone 2 into digital form, digital signal processing circuits including filters and amplifiers and an output converter supplying to the output transducer 3 a digital or analog output signal compensating for the users hearing impairment.

The switched capacitor voltage step down converter of the charge pump type illustrated in fig.

2 is of a type generally known from US-A-4,205,369 and comprises in series connection with a voltage source DC such as a hearing aid battery supplying a nominal voltage Ur, of about 1.3 V a converter configuration supplying an output voltage which is about half the nominal battery voltage. The converter circuit comprises a pair of transistors T1 and T2 shown as pand n-type MOSFET transistors, respectively, which are controlled by a control voltage v and connected with switch circuits S1 and S2, respectively, which may each be implemented as a pair of n- and p-type MOSFET transistors, respectively, controlled by opposite clock phases.

Transistors T1 and T2 and switch circuits S1 and S2 control charging and discharging of two capacitors Cf and C, as follows.

When the control voltage v is non-active or "low", transistor T1 is on and transistor T2 off and switch circuit S1 is inactive and switch circuit S2 active, so that capacitors Cf and C, are charged in series as shown in the equivalent diagram in fig. 3.

When the control voltage v is active or "high", transistor Tl is off and transistor T2 on and switch circuits Sl is active and switch circuit S2 inactive, so that capacitors Cf and C, are discharged in parallel to the load as shown in the equivalent diagram in fig.

4. In the diagrams in figs. 3 and 4 a load is represented by a resistor R1.

If capacitors Cf and C, are of equal capacitance the battery voltage U.c is divided into a half and the reduced supply voltage xU,, t will be about the half of the battery voltage.

In the configuration shown in fig. 5 three MOSFET transistors Ti, T2 and T3 and four switch circuits Sl, S2, S3 and S4 are connected to control the charging and discharging of three capacitors Cf, Cf 2 and Cs in the same way as described above.

When the control voltage v is "low" transistors T1 and T3 are on and transistor T2 off, while switch circuits S2 and S4 are active and switch circuits Sl and S3 inactive, so that capacitor C. is charged in series with the parallel connection of capacitors Cf and Cf2 as shown in the equivalent diagram in fig. 6.

When the control voltage v is "high" transistors ST and T3 are off and transistor T2 on, while switch circuits S2 and S4 are inactive and switch circuits Sl 25 and S3 active, so that the series connection of capacitors Cf and Cf 2 is discharged in parallel to the capacitor C, and the resistor R1 in parallel therewith as shown in the equivalent diagram in fig. 7.

If capacitors Cf 2 and C, are of equal capacitance the battery voltage Uc is divided into thirds and the reduced supply voltage xUout will be o0•. about the two thirds of the battery' voltage.

"The configurations shown in fig.s 2 and 5 are only examples of preferred embodiments of switched 35 capacitor charge pump converters for use in digital o* o *•go PCT/DK01/00007 WO 01/50812 7 hearing aids according to the invention. Within the scope of the invention one or more reduced operation voltages for different signal processing parts of the hearing aid can be obtained as fractions of the battery voltage.

As will follow from the description above the reduced operation voltage supplied by the voltage step-down converter of the invention will initially not be stabilized and will thus follow fluctuations of the battery voltage. It would obvious for an expert, however, to generate also a stabilized lower voltage, when needed, by means of a conventional stabilizing voltage regulator, while maintaining the benefit of a lower power consumption resulting from the invention.

Claims

1. A digital hearing aid comprising a microphone, an output transducer, a digital signal processor interconnected between the microphone and the output transducer and a power source including a standard hearing aid battery for the supply of operation voltage for said digital signal processor, characterized in that said digital signal processor comprises at least one integrated circuit signal processing part capable of operating at a reduced power supply voltage within a range below a nominal voltage of said battery and above a defined minimum voltage without significant change of performance, and wherein a switched step- down voltage converter is connected between the power source and said at least one signal processing part for providing said reduced power supply voltage.

2. The digital hearing aid as claimed in claim 1, characterized in that said at least one signal processing part is designed in CMOS technology.

3. The digital hearing aid as claimed in claim 1 or 2, characterized in that said at least one signal processing parts comprises parallel signal processing blocks, each operating at said reduced power supply voltage.

4. The digital hearing aid as claimed in claim 1 or claim 2 or claim 3, characterized in that said reduced power supply voltage is equal to or lower than *e o0.8 volt.

5. The digital hearing aid as claimed in any one of the preceding claims, 25 characterized in that said converter is a capacitive charge pump converter.

6. The digital hearing aid as claimed in claim 5, characterized in that said charge pump converter is designed to deliver two or more output voltages, at least one of which is said reduced power supply voltage. g*l*

7. The digital hearing aid as claimed in any one of the claims 1 to 4, characterized in that said voltage converter is a switched inductor network converter.

8. The digital hearing aid as claimed in any of one the preceding claims, characterized in that said reduced power supply voltage is an unstabilized voltage.

9. A digital hearing aid substantially as herein before described with reference to the accompanying figures. DATED this third day of November 2003 Widex A/S Patent Attorneys for the Applicant: F.B. RICE CO. too 0 .00. **to* es S a S 0 eastS